How can i make this code work?:(((

Question

The problem says you have 3 points a b c read through xoy coordinates and you have to determine if these points make a triangle. If not, show 'IMPOSIBIL'(impossible in romanian;)). I used this formula: AB=sqrt of (Ax-Bx)^2 + (Ay-By)^2. The compiler apparently has a proble. With the sqrt function. Any ideas why?
https://code.sololearn.com/cRjxVpmqEPf8/?ref=app

Answer 1

It tells you that the function is unkown.
Either implement sqrt on your own or more simple #include <math.h>